JPH0159710B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Electric heating devices, particularly in the form of bedding such as electric blankets, are becoming commonplace with consumers. It is important that such electrical heating devices have safe safeguards against overheating situations. Therefore, many overheating protection measures have been proposed for some time.

By the way, certification authorities that inspect the safety of electric heating devices such as electric blankets place particular importance on the safety of electric heating devices because they are often used by consumers.
It is strongly required that the circuit configuration of the electric heating device protects the user even if the circuit components are damaged.

Prior art patents include U.S. Pat. In addition to the lack of a reliable structure, there are certain difficulties in implementing a fail-safe circuit. Approval by the Certification Authority is therefore refused due to the risk of overheating, which would continue to supply electricity to the electric heating means in the event that a circuit component were to fail.

It is an object of the present invention to provide an electrical circuit having a semiconductor switch that senses an overheating situation and interrupts the supply of current, and wherein these semiconductor switches are adapted to effectively cut off the current even if a circuit component fails. The goal is to provide the following.

To achieve this objective, the present invention includes a pair of gate-controlled two-way semiconductor switches connected in series with each other and further connected in series with an electrical heating means. For more details,
The electric circuit of the electric heating device of the present invention includes an electric heating means that generates heat when an electric current flows through it, and an overheat protection means, and the overheat protection means is configured to heat the electric heating device in order to sense the occurrence of an overheating situation in the electric heating device. a temperature sensing negative characteristic impedance means thermally coupled to the means, and a pair of gated two-way semiconductor switches electrically connected in series with each other in a front-to-front orientation and connected in series with the electrical heating means. a capacitive connection means for capacitively connecting the gates of said pair of semiconductor switches to each other; and an electrical connection means for electrically connecting the gate of each semiconductor switch to the back of the other semiconductor switch via said temperature sensing negative characteristic impedance means. connection means, and in response to sensing an overheating condition by the temperature sensing negative characteristic impedance means, the temperature sensing negative characteristic impedance means triggers the semiconductor switch from a conducting state to a non-conducting state to connect the electrical heating means. and the capacitive connection means acts to prevent one of the semiconductor switches from triggering the other semiconductor switch to prevent the electrical heating means from being energized in the event of a short circuit condition. It is characterized by

Preferably, said temperature sensitive negative characteristic impedance means comprises a pair of conductors electrically separated from each other by a temperature sensitive dielectric material, said pair of conductors being disposed in close proximity to said electrical heating means. be.

Hereinafter, the present invention will be specifically described with reference to embodiments shown in the drawings. However, it will be apparent to those skilled in the art that various other modifications may be made to the structure described below while still achieving the desired effects of the present invention. Therefore, it is to be understood that the following description is not intended to limit the scope of the invention to this example.

FIG. 1 is a perspective view showing the electric heating device of the present invention in the form of bedding, particularly an electric blanket.

FIG. 2 is a diagram showing a part of the electric circuit used in the electric blanket of FIG. 1.

FIG. 3 is a diagram showing the remaining part of the electric circuit used in the electric blanket of FIG. 1.

FIG. 4 is a diagram for explaining the operation of a semiconductor switch under bias between terminals of the semiconductor switch.

FIG. 5 is a circuit corresponding to an integrated circuit of FIGS. 2 and 3, and is a diagram for explaining the direction in which current flows during a positive half cycle of alternating current.

FIG. 6 is a diagram similar to FIG. 5, and is a diagram for explaining the direction in which current flows during a negative half cycle of alternating current.

The electric heating device of the present invention is shown as bedding, particularly an electric blanket 10, as shown in FIG. Control housing 2 for adjusting the temperature as desired by the user
0 is provided separately from the electric blanket 10, one cable 30 of this control housing 20 is connected to the electric blanket 10, and the other cable 40 is connected to the electric blanket 10.
is connected to the power supply. The electrical circuitry within electric blanket 10 is shown in FIG. 3, and the electrical circuitry within control housing 20 is shown in FIG. electric blanket 1
The electrical circuits within 0 and within the control housing 20 may be separably connected as shown in U.S. Pat. No. 4,198,562. That is, the flat terminal on the right side of FIG. 2 and the flat terminal on the left side of FIG. 3 are detachably connected.

Referring to FIG. 3, the electric blanket 10 consists of an electric heating means 12 and a fibrous blanket outer shell 11 surrounding the electric heating means 12. The electric heating means 12 is composed of a resistance wire that generates heat when current flows through it. The electric blanket 10 further includes a temperature sensor 14 (eg, similar to that disclosed in US Pat. No. 3,222,497) as an overheat protection means. This temperature sensor 14 is arranged parallel to and thermally coupled to the electric heating means 12 and senses the occurrence of an overheating situation of the electric heating means 12. The temperature sensor 14 is of a temperature sensitive negative characteristic impedance type and includes a pair of conductors 1 electrically separated from each other by a temperature sensitive dielectric material.
It consists of 5 and 16. In addition, a pair of conductors 1
5 and 16 are capacitively coupled to each other. These are arranged in close proximity to the electric heating means 12 and are thermally coupled to the electric heating means 12.

Inside the control housing 20, there are provided a temperature setting device that can be freely selected to the temperature desired by the person using the electric blanket 10, a pair of gate-controlled two-way semiconductor switches 25 and 26, and a power switch 24. . Temperature setting device is bimetal switch member 2
1 and a compensation heater 22. The temperature setting device is not limited to this, and may have other forms (for example, as disclosed in US Pat. No. 3,588,446).

The gated two-way semiconductor switches 25, 26 used in the device of the present invention are commonly known as "quadracs".
It is available on the market. A quadruck is a bistable semiconductor device that can be triggered by an integrated diode to interrupt voltage in either direction.
By passing current in either direction and applying a gate signal, it is triggered to pass current in either direction. A quadruple generally consists of a terminal MT ₁ , an adjacent gate terminal G located on the same side, and a terminal MT ₂ located on the other side. Terminal MT ₁
The semiconductor region between and MT ₂ is in the form of a pair of parallel semiconductor switches. The regions of such a pair of parallel semiconductor switches are indicated by a pair of inverted triangular abbreviations. The gate is indicated by a line as Gate Terminal G. semiconductor switch 25,
A pair of inverted triangles are shown within the gate portion of 26, which have the diac or diode characteristics of a semiconductor switch. Terminal MT ₁ is gate Terminal G and Terminal
This is the reference point when measuring voltage and current at MT ₂ . Note that the terminal MT ₁ side is considered the "front" of the semiconductor switch, and the terminal
The side of MT ₂ is considered "back". Therefore, this terminology is used herein to facilitate describing the interconnection of the pair of semiconductor switches 25, 26. As shown in FIGS. 2, 5 and 6, a pair of gate-controlled two-way semiconductor switches 25 and 26 according to the present invention are connected in series and front to back. This is called front-to-front orientation. And these front-to-front oriented semiconductor switches 25, 2
6 is connected in series to electric heating means 12.
Thus, the power switch 24 and the compensation heater 2
2. The bimetallic switch member 21, the electric heating means 12, the semiconductor switch 26, and the semiconductor switch 25 are connected in series.

Further, each gate terminal G of the semiconductor switches 25 and 26 is connected to the temperature sensor 14. The temperature sensor 14 consists of conductors 15, 16 having a temperature sensing negative characteristic impedance. This temperature sensor 14 includes a resistor and a capacitor 28. The other ends of the conductors 15 and 16 are crossed and connected to terminals _MT2 of other semiconductor switches, respectively. That is, the gate terminals G of the semiconductor switches 25 and 26 are respectively connected to the terminal MT ₂ of the other semiconductor switch via the conductors 15 and 16 having temperature-sensitive negative characteristic impedance. Thus, in normal operation, the gating signals from conductors 15, 16 of temperature sensor 14 trigger semiconductor switches 25, 26 such that the applied alternating current passes through electrical heating means 12 on every cycle. However, when an overheating situation occurs, the impedance value of temperature sensor 14 changes, lowering the gate signal to a level that does not trigger semiconductor switches 25, 26 into conduction.
Therefore, the semiconductor switches 25 and 26 become non-conductive, and no current flows to the electric heating means 12.

Further, gate terminals G of a pair of semiconductor switches 25 and 26 are coupled to each other via a capacitor 28. Thus, semiconductor switch 2
If one of the semiconductor switches 5 and 26 becomes conductive and fails, the other semiconductor switch becomes non-conductive and no current flows to the electric heating means 12.

This is because semiconductor switches 25 and 26 must be triggered at the same time. Otherwise, the circuit will not work properly. capacitor 2
8 is provided for triggering at the same time, and is charged during the non-conducting period of the semiconductor switches 25 and 26, and discharges its energy when triggered. However, if one semiconductor switch fails in a conductive state, capacitor 28 will not be charged to simultaneously trigger the other semiconductor switch. This is a current path with some resistance, that is, an electrical connection means (conductors 15, 16)
This is why it extends from the rear terminal MT ₂ to the gate of the failed semiconductor switch. Therefore, there is no current to charge capacitor 28. Thus, during a failure of the semiconductor switch, current to the electrical heating means 12 is interrupted by capacitive coupling and "cross-connection". It is clear that if either of the semiconductor switches 25, 26 becomes non-conductive and fails, no current will flow to the electric heating means 12.

Now, FIG. 4 is a diagram for explaining the characteristics of the quadratic, and is a diagram divided into four quadrants to explain the relationship between the voltage applied to the rear terminal _MT2 and the current passing through the gate G. That is, the vertical coordinate in this diagram indicates whether the voltage applied to the rear terminal MT ₂ is positive or negative, and the horizontal coordinate indicates the direction of the current through the gate, and each quadrant has a different operating state. . For example, in the fourth quadrant,
The current through the gate is positive and the rear terminal
The voltage applied to MT ₂ is also positive.

Based on FIG. 4, FIGS. 5 and 6 are diagrams showing how the function of the semiconductor switch, which is the overheat protection means of the present invention, changes depending on the alternating current applied to the electric heating device. Note that the circuit shown in FIG. 5 or 6 is equivalent to a circuit in which the circuit shown in FIG. 2 and the circuit shown in FIG. 3 are connected. As can be seen from these figures, the semiconductor switch changes every half cycle of one AC cycle.
Figure 5 shows the AC applied to this electric heating device.
Semiconductor switches 25, 26 during the positive half cycle
Of the pair of semiconductor switches, the one shown at the top is in the state of the quadrant shown in Figure 4 due to the voltage at point A, and the one shown at the bottom is at point B. The voltage is in the fourth quadrant. The current then flows through the gates G1 and G2 in the direction indicated by the dotted arrow. FIG. 6 shows the situation during the subsequent negative half cycle, with the semiconductor switch shown at the top being in the quadrant state and the semiconductor switch below being in the quadrant state, with the current flowing in the opposite direction to the gate G1. , G2.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the electric heating device of the present invention in the form of bedding, particularly an electric blanket. FIG. 2 is a diagram showing a part of the electric circuit used in the electric blanket of FIG. 1. FIG. 3 is a diagram showing the remaining part of the electric circuit used in the electric blanket of FIG. 1. FIG. 4 is a diagram showing the operation of a semiconductor switch under bias between terminals of the semiconductor switch. FIG. 5 is a circuit corresponding to an integrated circuit of FIGS. 2 and 3, and is a diagram for explaining the direction in which current flows during a positive half cycle of alternating current. FIG. 6 is a diagram similar to FIG. 5, and is a diagram for explaining the direction in which current flows during a negative half cycle of alternating current. In the figure, 10 is an electric blanket, 11 is a fibrous blanket outer shell, 12 is an electric heating means, 14 is a temperature sensor, 15 and 16 are conductors, 20 is a control housing,
21 is a bimetal switch, 22 is a compensation heater, 24 is a power switch, 25 and 26 are semiconductor switches, and 28 is a capacitor.

Claims (1)

[Scope of Claims] 1. An electric heating device protected against overheating and switch damage conditions, comprising an electric heating means that generates heat when current flows through it, and an overheating protection means, the overheating protection being protected against overheating and switch damage. means are electrically connected in series with each other in a front-to-front orientation with temperature sensing negative characteristic impedance means thermally coupled to the electrical heating means for sensing the occurrence of an overheating situation in the electrical heating device; a pair of gate-controlled two-way semiconductor switches connected in series with said electric heating means for controlling the current passing through said electric heating means; and capacitive coupling means for capacitively coupling the gates of said pair of semiconductor switches to each other. and electrical connection means for electrically connecting the gate of one of the semiconductor switches through the temperature sensing negative characteristic impedance means to the back of the other semiconductor switch, the temperature sensing negative characteristic impedance means detecting overheating conditions. In response to sensing, the temperature sensitive negative characteristic impedance means triggers the semiconductor switch from a conducting state to a non-conducting state to prevent energization of the electrical heating means, and the capacitive coupling means triggers the semiconductor switch An electric heating device with overheat protection, characterized in that it acts to prevent triggering of the other semiconductor switch in order to prevent energization of the electric heating means when one of the devices is short-circuited. 2. The temperature sensitive negative characteristic impedance means comprises a pair of conductors electrically separated from each other by a temperature sensitive dielectric material, the pair of conductors being connected to the electrical heating means in order to sense the occurrence of overheating in the electrical heating device. An electric heating device with overheat protection according to claim 1, which is arranged closely adjacent to each other.